The present invention relates to automotive vehicles, and more particularly to powertrain control of automotive vehicles.
It is known to determine minimum allowed airflow based on engine misfire conditions. Minimum airflow is typically determined based on operating conditions such as ignition timing. It is also known to limit actual airflow to this minimum value in electronic throttle control systems. An advantage is that it is possible to obtain minimum engine torque while not shutting off cylinders. Such a system is described in U.S. Pat. No. 6,039,023.
The inventors herein have recognized several disadvantages with this approach. For example, a disadvantage occurs when operating at low airflows, such as the minimum allowed airflow. If the engine speed drops below the idle speed control region, the engine controller will then try to increase airflow to maintain engine speed at least at the desired idle speed. However, since airflow is a relatively slow engine torque actuator due to manifold filtering delays (which are maximum at low engine speeds), engine speed may actually drop significantly below the desired idle speed before it increases back up to the desired speed.
Disadvantages of prior approaches are overcome by a method for controlling an internal combustion engine of a vehicle. The method comprises determining a minimum allowed air amount based on operating conditions, detecting engine speed of the engine, determining a required air amount for operating at a desired engine speed, and when said minimum allowed air amount is less than said required air amount, increasing said minimum allowed airflow as detected engine speed approaches said desired engine speed from above.
By increasing airflow in this way, it is possible to minimize drops in engine speed due to the slow torque actuation of engine airflow. In other words, operation according to the present invention prevents situations from occurring where a rapid decrease of engine speed toward idle speed results in an engine speed dip below the desired idle speed. However, according to the present invention, it is still possible to operate at low airflows during non-idle conditions and obtain benefits there from such as reduce fuel consumption.